Research paper summary – Casril Liebert

Observational study of the effect of obesity on lung volumes

Joerg Steier, Alan Lunt, Nicholas Hart, Michael I Polkey, John Moxham

Published in the journal Thorax, April 2014

With a rise in obesity, a bigger effort must be made to understand all the factors and effects of obesity on the human body. It is already known that obesity is associated with an increase in work of breathing and neural respiratory drive (the muscular effort required to breathe), as well as changes in lung capacities. It can also cause hypercapnic respiratory failure which is when there’s too much carbon dioxide in the blood. However, the effects on the mechanics of breathing are unclear. This study attempts to measure the effect of obesity on lung volume and various pressures in the chest and better understand the physiological differences between different weight people.

9 obese people and 9 normal weight people volunteered to be measured whilst seated and whilst lying on their back. During the study, the subjects breathed into the mouthpiece of a machine called a spirometer which monitors the speed and volume of air movement into and out of the lungs. Pressures in the chest and abdomen were also measured, along with the amount of air remaining in the lungs after a breath out (functional residual capacity, or FRC).

After evaluating results, it was noted that high pressures in the chest are have an important role in the mechanisms of the respiratory system. The chest and abdomen pressures were found to be much higher in the obese group, and the FRC lower. The strength of the breathing muscles were measured and the result showed that the obese group had weaker muscles. There was a direct relationship seen between subjects’ waist circumference and the chest and abdominal pressures, as well as with the drop in FRC.

One of the main conclusions is that gastric and oesophageal pressures correlated with waist size, since the obese group had significantly higher pressures. One can deduce from this result that these high pressures are inhibiting efficient function of the lungs, and contributing to the reduced volume of air in the lungs. To bring this research into practical everyday healthcare, more could be done to attempt to reduce abdominal pressures in obese patients. By doing so with appropriate treatment in the future, obese people may be able to reach normal lung function, thereby reducing the number of patients suffering from breathlessness and sleeping disorders from respiratory problems.

This summary was produced by Casril Liebert, Year 13 student from JFS School, Harrow, as part of our departmental educational outreach programme.